The present invention relates to a composite fabric (a mixed fabric) composed of reinforcing yarns and thermoplastic resin yarns which is suitable to be used as a laminating material for making fiber-reinforced thermoplastic resin laminates.
Fiber-reinforced thermoplastic resin materials have been used in various fields and methods for production thereof are explained below with reference to thermoplastic resin reinforced by glass fiber which is a typical material.
(1) Chopped glass fibers of 3-6 mm in length are mixed with a resin and kneaded with heating into compound. This compound is molded by an injection molding machine.
(2) Continuous glass fibers are impregnated and coated with a heat molten resin. This coated fibers are cut to 3-6 mm in length and suitably made into a compound comprising mixture of the fibers and the resin, which is molded by an injection molding machine.
(3) A chopped strand mat is previously made from chopped glass fibers of 2.5-5.0 mm and is impregnated with a molten resin to make a sheet-like compound, which is molded by compression molding under heating.
(4) Continuous glass fibers arranged in the form of sheet or a glass fiber fabric is impregnated with a molten resin or a resin dissolved in a solvent, followed by evaporation of the solvent and drying and then making it into a sheet-like compound, which is molded by compression molding under heating.
(5) Glass fibers and thermoplastic resin fibers are subjected to intermingling to produce hybrid yarns, from which a fabric is made and the fabric is heated to melt the thermoplastic resin fibers. Then, this fabric is compression molded. (cf. Japanese Patent Unexamined Publication (Kokai) No. 130345/86).
However, these conventional methods all have problems as explained below.
(1) It is difficult in case of injection molding method to increase the content of reinforcing glass fibers to more than 30% by weight. Besides, molded articles are limited to those of small size.
(2) According to compression molding under heating, sufficient pressure cannot be applied to the sheet-like compound made by impregnating a chop mat with molten resin and glass fibers arranged in the form of sheet impregnated with resin because glass fibers drift together with resin and as a result, bubbles are entrapped in the molded articles.
In order to prevent the retention of bubbles, the compound must be put in a mold to prevent drifting of the glass fibers and thus, moldability becomes inferior.
(3) According to the method of making glass fibers and thermoplastic resin fibers into a yarn by intermingling and making a fabric therefrom, cost is increased due to the additional one step of intermingling and there are difficulties in doubling and weaving because the yarn is composite yarn of different materials.
These problems are serious not only in use of glass fibers as reinforcing fiber, but also in use of carbon fibers or aramide fibers.